1. Field of the Invention:
This invention relates to a membrane type artificial lung and to a method for the manufacture thereof. More particularly, it relates to a membrane type artificial lung adapted to remove carbon dioxide gas from the blood and add oxygen to the blood during the extra-corporeal circulation of blood. The artificial lung excels in gas-exchange ability, particularly in the ability to remove carbon dioxide gas, which precludes the possibility of leakage of blood plasma even during a protracted service, exhibits high biocompatibility, and experiences a minimal loss of platelets, and to a method for the manufacture thereof.
2. Description of the Prior Art:
Heretofore, as an auxiliary means for a cardiotomy, a membrane type artificial lung is adapted to effect the exchange of gases by exposing the blood in circulation to an oxygen-containing gas through the medium of a gas-exchange membrane possessed of a satisfactory permeability to gas has been known. This gas-exchange membrane is required, in addition to having satisfactory permeability to gas, to exhibit high mechanical strength, to avoid inducing leakage of blood plasma during a protracted circulation of blood, and does not inflict on the blood any injury manifested in the form of blood coagulation, formation of microthrombosis, loss of platelets, degeneration of blood plasma proteins, or hemolysis. The gas-exchange membranes which are currently used in the membrane type artificial lungs are of two major types; homogeneous membranes and porous membranes. As homogeneous membranes, silicone membranes are predominantly used. In contrast, porous membranes are made of various materials such as, for example, polyethylene, polypropylene, polytetrafluoroethylene, polysulfones, polyacrylonitrile, polyurethane, and polyamides. The homogeneous silicone membranes, owing to a deficiency in strength, are not produced in any smaller wall thickness than 100 .mu. m, and therefore possess limited permeability to gas, and are particularly deficient in permeability to carbon dioxide gas. When tens of thousands of hollow fiber membranes of silicone are bundled to acquire a desired gas-exchange ability and the bundle is used in place of a plain homogeneous silicone membrane, the apparatus using this bundle proves disadvantageous in that the apparatus has to be large in order to accommodate the bundle, the volume of priming is proportionately large, and the bundle is costly. The porous membranes possess numbers of minute pores penetrating the membranes in the direction of wall thickness. Since the membranes are hydrophobic, they do not permit the passage of blood plasma through the minute pores thereof, namely they do not experience leakage of blood plasma therethrough from the blood conduit side to the gas conduit side, and they accordingly permit the addition of oxygen from the feed gas to the blood and the removal of carbon dioxide gas from the blood into the effluent gas. The porous membranes, however, are degraded by dew because of their high permeability to steam, and at times experience leakage of blood plasma during a protracted use in blood circulation. This phenomenon is witnessed even in porous membranes which in a test for water leakage conducted during the course of the manufacture of artificial lungs, which were confirmed to be free from such problems. Thus, this is a phenomenon which takes place during use. Only a few of the materials of which the porous membranes are made are satisfactory from the viewpoint of the biocompatibility, as evidenced by the loss of platelets.
For the purpose of overcoming the various drawbacks of the porous membrane as described above, we have proposed an artificial lung having the minute pores in the porous membrane blocked with silicone oil (Japanese Patent Application SHO No. 58(1983)-92,325) and an improved artificial lung having the minute pores in the porous membrane blocked with silicone rubber (Japanese Patent Application SHO No. 59(1984)-105,384). The artificial lung having the minute pores in the porous membrane blocked with silicone rubber has eliminated the problem of blood plasma leakage experienced by the conventional artificial lung using an ordinary porous membrane. In terms of the ability to remove carbon dioxide gas, however, the artificial lung is not satisfactory. For example, it has effected the removal of the amount of carbon dioxide gas produced at all in the patient's living body with a small amount of extra-corporeal circulation of the blood as in ECCO.sub.2 R (extra-corporeal CO.sub.2 removal) with difficulty.
An object of this invention, therefore, is to provide a novel membrane type artificial lung and a method for the manufacture thereof.
Another object of this invention is to provide a membrane type artificial lung capable of removing carbon dioxide gas from the blood and adding oxygen to the blood during the extra-corporeal circulation of the blood, in which the membrane type artificial lung excels in the ability to exchange gases, precludes the possibility of leakage of blood plasma during a protracted use, exhibits high biocompatibility, experiences the loss of platelets only nominally and a method for the manufacture thereof.
Yet another object of this invention is to provide a membrane type artificial lung most suitable for ECCO.sub.2 R and a method for the manufacture thereof.